Electrical power lines often run through heavily wooded areas, either in neighborhoods or in rural areas. Normally a path, or right of way, is cut through such wooded areas to make way for the power lines, but eventually the trees or other vegetation will encroach upon this path and it will need to be trimmed back. For example, tree limbs, over time, may grow over the power lines, presenting the risk of damaging the lines should the limbs fall or make contact with the lines during a storm. Typically, such trimming is required every five years or so, although this time period may be shorter or longer in a given area. Because power lines often span long distances, such as hundreds of miles, a trimming operation may be a complex and time intensive endeavor for which efficiency is a consideration. Two different types of approaches have been used in the prior art. Typically, to trim around transmission lines (which go cross country) a rough cutting and partially automated mechanism has been used. Alternatively, in residential/commercial areas serviced by electrical distribution lines a manual approach has been utilized.
In one common manual approach, a mobile unit such as an “insulated bucket truck” is utilized. The bucket truck has an insulated bucket or basket connected to an insulated boom (crane like structure), which is in turn connected to the chassis of the truck. The bucket (or “basket” as it is sometimes known) contains room for a worker and associated tree trimming equipment, such as a hand operated chainsaw or hydraulic pole saw. Once in the bucket, the worker may be lifted up to an appropriate height and location to trim the trees. Thus, the worker can manually cut tree limbs to combat encroachment of the trees toward the power lines. This approach, however, is not optimal for several reasons. The manual approach is slow, involves potential risk of injury to the worker and associated potential liability, and might allow the cut refuse to fall freely and dangerously to the ground. Alternatively, the cut refuse may be manually lowered with a rope to the ground below, but this is slow and cumbersome.
Improvements over the bucket technique have been introduced in the prior art, such as that described in U.S. Pat. No. 5,501,257 (the '257 patent), which is incorporated by reference in its entirety. The '257 patent describes a boom with a mountable assembly on the end instead of a bucket. The assembly contains jaws for clamping a tree limb to be cut and a saw arm for cutting the grasped limb. The assembly can spin the saw arm around the axis formed by the boom to allow the jaws to be brought into alignment with a tree limb and then rotate the saw arm in a circular fashion to cut the clamped limb. After cutting, the saw blade may be retracted and, in theory, the cut tree limb will be held in place by the jaws, which will then allow the operator to place the cut limb on the ground for disposal.
Another prior art practice relating to tree clearance around electrical lines involves the trimming of tree limbs and administration of herbicides or wound dressing to impede future tree growth. Herbicides administered using the bucket technique described above suffer from concerns about the health and safety of the aerial worker falling or coming into contact with dangerous herbicides or inadvertent electric shock when a liquid comes in contact with a power line. An automated distribution of herbicides from an apparatus at the end of a boom represents an improvement over the bucket technique and is described in U.S. Pat. No. 6,990,770 which is hereby incorporated by reference herein.
As explained above, certain prior art techniques have been used to provide an efficient yet somewhat non-precise solution to cutting of tree limbs and other foliage around rights of way. In particular, prior art approaches are limited with respect to a comprehensive axial rotation of an aerial tool assembly. Additionally, prior art solutions are usually limited in the amount of reconfiguration available in the field for the entire tool apparatus attached to the distal end of the aerial boom. Therefore, it would be desirable to provide a more precise and possibly field configurable apparatus for trimming foliage around power lines and other areas where automated, yet precise trimming may be desired. Additional applications (e.g., other than tree-trimming) are also possible. In general, a solution is needed for performing automated aerial tasks from a ground based vehicle in a more field-configurable manner. This disclosure presents several embodiments of such a solution.